Fixes to PHP version dependancy

Lowest PHP version now 5.5.

Some CS fixes, and a little refactoring (renaming a trait).

Removed a duplicate trait usage in AbstractRedirectRequest, which was failing travis on PHP 5.5 only.

Support lightbox mode

The lightbox mode is configured and works in the same way as the redirect mode, but uses and iframe drawn using JavaScript in a darkened mask to give the appearance of staying on the merchant site.

The main difference is a custom method providing the required HTML fragments for the lightbox rendering template.

Support PayPal ItemBag

Just supports the standard OmniPay Itembag for now, with tax and shipping amounts zeroed out.

Additional PayPal support

Supports PayPal orders (treated as a cardReference)

Inline mode, further optional parameters

2.0.2

Add further optional parameters; inloine/iframe support.

Offline authorize/purchase implemented

Still just for testing. What is documented is working, but some refactoring and possible design changes are likely.

Release for testing

There is still a large TODO list. However, this version supports simple payments using the redirect mode.